Contact printing using high volume presses is commonly employed to print a large number of copies of an image. Contact printing presses utilize printing plates to sequentially apply colorants to a surface to form an image thereon. The surface can form part of a receiver medium (e.g. paper) or can form part of an intermediate component adapted to transfer the colorant from its surface to the receiver medium (e.g. a blanket cylinder of a press). In either case, a colorant pattern is transferred to the receiver medium to form an image on the receiver medium.
Printing plates typically undergo various processes to render them in a suitable configuration for use in a printing press. For example, exposure processes are used to form images on an imageable surface of a printing plate that has been suitably treated so as to be sensitive to light or heat radiation. One type of exposure process employs masks. The masks are typically formed by exposing highly sensitive film media using a laser printer known as an “image-setter.” The film media can be additionally developed to form the mask. The mask is placed in area contact with a sensitized printing plate, which is in turn exposed through the mask. Printing plates exposed in this manner are typically referred to as “conventional printing plates.” Typical conventional lithographic printing plates are sensitive to radiation in the ultraviolet region of the light spectrum.
Another conventional method directly forms images on printing plates through the use of a specialized imaging apparatus typically referred to as a plate-setter. A plate-setter in combination with a controller that receives and conditions image data for use by the plate-setter is commonly known as a “computer-to-plate” or “CTP” system. CTP systems offer a substantial advantage over image-setters in that they eliminate film masks and associated process variations associated therewith. Printing plates imaged by CTP systems are typically referred to as “digital” printing plates. Digital printing plates can include photopolymer coatings (i.e. visible light plates) or thermo-sensitive coatings (i.e. thermal plates).
In order to provide printed materials of suitable quality during a printing operation, the images formed on the printing plate must be accurately registered. Typically, in computer-to-plate imaging systems, one or more edges of a printing plate are used for registration purposes during the formation of the images. For example, during an image forming procedure, a printing plate is aligned on an imaging support surface of a computer-to-plate system by bringing one of its edges known as a “registration edge” into contact with various registration members. Conventional computer-to-plate registration systems typically have a number of registration pins or stops fixedly attached to the imaging support surface. Various groupings of fixed registration pins are often employed to register printing plates of different sizes or to register multiple printing plates.
Although these conventional fixed pin registration systems are relatively simplistic in nature, various problems are associated with them. For example, limited surface contact between a printing plate's registration edge and the fixed pins is usually established as the printing plate is moved into engagement with the pins. Ever increasing throughput demands placed on the computer-to-plate system require that the printing plate be conveyed with increasing speeds. These increased conveyance speeds can increase loading conditions between the printing plate's registration edge and the fixed pins and impart deformations or other damage onto the registration edge of the printing plate.
Edge deformations or damage can lead to various problems. For example, once the printing plate is registered against the registration pins it is imaged typically in accordance with various offsets from the various printing plate edges. Deformations such as small dents in the vicinity of the contacted registration pins can cause shifts in a desired image placement with respect to the registration edge. Additional printing plate preparation steps can include punching and bending procedures which are used to impart various features onto the printing plates to facilitate the mounting and registration of the printing plates on press. If these features are added by equipment that uses a registration system that engages with deformed areas of the registration edge, the desired positioning of these features can be adversely impacted. In some systems, punching capabilities are incorporated in the computer-to-plate system itself.
Other factors can also lead to the formation of deformations on various edges of a printing plate. For instance, there is an increasing demand for computer-to-plate systems that can accommodate larger plate sizes. The increased size and weight associated with these larger printing plates requires larger conveyance forces to move the printing plate into engagement with conventional registration pin systems. These increased forces can further lead to the formation of registration edge deformations.
Thus, there is a need for an imaging apparatus with improved plate registration capabilities. There is also a need for a computer-to-plate imaging system adapted to improve the positioning printing plates to form images accurately thereon. In addition, there is a need for a computer-to-plate system with a printing plate registration system that reduces the potential to form undesired deformations on the edges of printing plates during the handling thereof.